Lanoxin (digoxin) is a time-tested cardiac glycoside derived from the leaves of Digitalis lanata. It remains a cornerstone in the management of various heart conditions, primarily for its positive inotropic and negative chronotropic effects. This medication increases the force of myocardial contraction while slowing the heart rate, making it invaluable for treating heart failure and controlling ventricular response in atrial fibrillation. Its narrow therapeutic index necessitates careful dosing and monitoring under expert medical supervision to maximize efficacy and minimize risks.

Features

• Active Ingredient: Digoxin
• Therapeutic Class: Cardiac Glycoside
• Mechanism of Action: Inhibition of the sodium-potassium ATPase pump, leading to increased intracellular sodium and calcium, which enhances myocardial contractility (positive inotropy) and vagal tone, slowing conduction through the atrioventricular (AV) node.
• Available Formulations: Oral tablets (e.g., 62.5 mcg, 125 mcg, 250 mcg) and injectable solution for IV or IM administration.
• Bioavailability: Oral tablets have approximately 60-80% bioavailability.
• Onset of Action: Oral: 1-2 hours; Peak effect: 6-8 hours. IV: 5-30 minutes; Peak effect: 1-4 hours.
• Half-life: 36-48 hours in patients with normal renal function (prolonged in renal impairment).
• Primary Excretion: Renal (mostly unchanged drug).

Benefits

• Enhances Cardiac Output: Strengthens the heart’s pumping action, improving ejection fraction and alleviating symptoms of heart failure such as dyspnea and fatigue.
• Controls Ventricular Rate: Effectively slows the heart rate in patients with atrial fibrillation and atrial flutter, improving ventricular filling and coronary perfusion.
• Long Half-Life for Stable Dosing: Allows for once-daily maintenance dosing in most patients, promoting adherence and stable serum levels.
• Oral and Parenteral Options: Provides flexibility in administration for both outpatient management and acute inpatient care.

Common use

Lanoxin is indicated for the treatment of mild to moderate heart failure in adult patients. It is also used to control resting ventricular rate in patients with chronic atrial fibrillation, helping to maintain a more controlled and efficient heart rhythm. Its use is typically part of a comprehensive treatment plan that may include diuretics, ACE inhibitors, and beta-blockers.

Dosage and direction

Dosing is highly individualized and MUST be determined by a physician based on the patient’s age, weight, renal function, and clinical condition. A loading dose (digitalization) may be used to achieve a therapeutic effect rapidly, followed by a lower daily maintenance dose.

• Maintenance Dosing (Adults with Normal Renal Function): The typical daily maintenance dose ranges from 125 mcg to 250 mcg (0.125 mg to 0.25 mg) orally, taken once daily at the same time each day.
• Loading Dose (Digitalizing Dose): May be administered in divided doses over 24 hours (e.g., 500-1000 mcg total) under close medical supervision to achieve rapid therapeutic effect.
• Geriatric Patients and Those with Renal Impairment: Require significantly lower doses (e.g., 62.5 mcg daily or every other day) due to reduced clearance. Dosing is often guided by ideal body weight and creatinine clearance calculations.
• Administration: Tablets should be taken with or without food, consistently. The IV formulation is reserved for urgent situations and must be administered slowly.

Regular monitoring of serum digoxin levels is critical. The therapeutic range is generally 0.5 to 2.0 ng/mL, though clinical response is the ultimate guide. Levels should be drawn at least 6-8 hours after the last dose.

Precautions

• Renal Impairment: Digoxin is primarily excreted by the kidneys. Dosage MUST be reduced in patients with renal insufficiency to prevent toxic accumulation. Creatinine clearance must be calculated regularly to guide dosing.
• Electrolyte Imbalances: Hypokalemia, hypomagnesemia, and hypercalcemia predispose patients to digoxin toxicity, even at therapeutic serum levels. Electrolyte levels must be monitored and corrected, especially when concomitant diuretics are used.
• Thyroid Disorders: Both hypothyroidism and hyperthyroidism can alter sensitivity to digoxin. Dose adjustments may be necessary.
• Monitoring: Requires frequent clinical assessment (for symptoms and signs of efficacy/toxicity), electrocardiograms (ECGs), and serum digoxin level monitoring, especially after initiation or dose changes.
• Pregnancy and Lactation: Category C. Should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus. Digoxin is excreted in breast milk; caution is advised.

Contraindications

Lanoxin is contraindicated in patients with:

• Ventricular fibrillation.
• Known hypersensitivity to digoxin or other digitalis preparations.
• Second- or third-degree atrioventricular (AV) block (unless a permanent pacemaker is in place).
• Wolff-Parkinson-White (WPW) syndrome, as it may accelerate accessory pathway conduction.
• Constrictive pericarditis and cardiac amyloidosis.

Possible side effect

Side effects are often dose-related and may be signs of toxicity.

• Common: Nausea, vomiting, diarrhea, headache, dizziness, fatigue, visual disturbances (e.g., yellow-green halos around objects, blurred vision).
• Cardiac (Serious): New arrhythmias are the most dangerous manifestation of toxicity. These include premature ventricular contractions (PVCs), ventricular bigeminy or trigeminy, paroxysmal atrial tachycardia with block, AV block, and ventricular tachycardia or fibrillation.
• Other: Rash, gynecomastia (rare).

Drug interaction

Lanoxin has numerous significant interactions. A healthcare provider must review all concomitant medications.

• Diuretics: Potassium-wasting diuretics (e.g., furosemide, hydrochlorothiazide) can cause hypokalemia, increasing the risk of toxicity.
• Antiarrhythmics: Quinidine, verapamil, amiodarone, and dronedarone can significantly increase serum digoxin concentrations.
• Macrolide Antibiotics: Erythromycin and clarithromycin can increase digoxin levels.
• Antacids & Colestyramine: Can decrease the absorption of oral digoxin (separate administration by at least 2 hours).
• Beta-blockers and Calcium Channel Blockers: Have additive effects on AV node conduction, increasing the risk of bradycardia and heart block.
• Sympathomimetics: May increase the risk of arrhythmias.
• Succinylcholine: May potentiate its effects and lead to arrhythmias.

Missed dose

If a dose is missed, it should be taken as soon as it is remembered on the same day. If it is almost time for the next scheduled dose, the missed dose should be skipped. The patient should never take a double dose to make up for a missed one, as this can precipitate toxicity. Patients should be instructed to inform their doctor about any missed doses, especially before having a serum digoxin level drawn.

Overdose

Digoxin overdose is a life-threatening medical emergency. Toxicity can occur with only a slight elevation above the therapeutic range, especially in the presence of risk factors.

• Symptoms: Severe nausea and vomiting, hyperkalemia, profound bradycardia, visual changes, confusion, and life-threatening cardiac arrhythmias.
• Treatment: Requires immediate hospitalization. Management includes:
  • Discontinuation of digoxin.
  • ECG and continuous cardiac monitoring.
  • Correction of electrolyte imbalances (e.g., potassium, magnesium).
  • Administration of digoxin-specific antibody fragments (Digibind®/DigiFab®), which are the definitive antidote for severe, life-threatening toxicity.
  • Management of arrhythmias with appropriate medications (e.g., phenytoin, lidocaine) or pacing.

Storage

• Store at room temperature (20°C to 25°C or 68°F to 77°F).
• Protect from light and moisture.
• Keep in the original container, tightly closed.
• Keep all medications out of the reach of children and pets.

Disclaimer

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition or before starting or stopping any medication. Never disregard professional medical advice or delay in seeking it because of something you have read here. The author does not recommend or endorse any specific tests, physicians, products, procedures, opinions, or other information that may be mentioned.

Reviews

“Lanoxin remains an essential tool in our cardiology arsenal. Its ability to provide both rate control and inotropic support in a single agent is unique. While its narrow therapeutic window demands respect and vigilance, its efficacy in managing chronic AFib and heart failure, particularly in older populations, is well-established. The key to its safe use is meticulous patient selection, individualized dosing based on renal function, and unwavering commitment to therapeutic drug monitoring.” – Cardiologist, 15 years of experience

“For many of my heart failure patients, the addition of a carefully titrated dose of digoxin has been the difference between being housebound and having functional capacity. It’s a drug that teaches humility; you must always be aware of its potential for toxicity, but when used correctly, the benefits are undeniable.” – Heart Failure Specialist Nurse Practitioner